Police barricade tape surrounds Arapahoe High School after a shooting incident in Centennial, Colorado December 14, 2013. Police were looking into the motive of a student who opened fire at the school on December 13, 2013, severely wounding a teenager before apparently killing himself, as the U.S. state sought to understand the latest in a series of shootings.

The 18-year-old teen, Karl Halverson Pierson, who shot and critically wounded a fellow student at a suburban Denver high school on Friday, had an "evil intent to harm multiple individuals," officials said Saturday as the investigation continued.

"His intent was evil and his evil intent was to harm multiple individuals," NBC quoted Arapahoe County Sheriff Grayson Robinson as saying, of Pierson, who opened fire inside Arapahoe High School in Centennial, Colo., before turning the gun on himself on Friday.

The shooter used a shotgun, which he bought legally, while also carrying multiple rounds of ammunition strapped across his body, a machete and a backpack filled with three Molotov cocktails, USA Today reported.

"It is our strong belief that (Pierson) came to this school ... to utilize those multiple rounds to cause harm to a large number of individuals," Robinson was quoted as saying at a news briefing Saturday afternoon.

Robinson also said Pierson failed to shoot more people because a sheriff's deputy assigned to the school got to the area quickly. "The shooter knew the deputy was in the area," he said. "We believe that the response ... was absolutely critical to the fact that we did not have additional injury or deaths."

However, Pierson shot Claire Esther Davis, a 17-year-old student, "point blank" in the face, just because she was sitting nearby with a friend. She suffered severe head trauma. "I believe Claire Davis is an innocent young lady," Robinson said.

Davis' condition remained critical Saturday, and she was admitted to Littleton Adventist Hospital, according to a statement by her family. "Our beautiful daughter Claire Davis has severe head trauma as a result of a gunshot. She needs your continued prayers," the statement read.

Hundreds of students from the school gathered for a candlelight vigil at Arapaho Park in Centennial, not far from the school, on Saturday night to pray for Davis, Denver Post reported.

"We just thought it would be a good idea to get everyone together to pay respect to Claire, as well as gather with other people going through the same thing," Maggie Hurlbut, an Arapahoe senior, was quoted as saying.

A neighbor of the victim was quoted as saying that she was the best babysitter in the community. "She took care of our 5-year-old. She was well-loved. I believe she wanted to go into nursing - I know she had already been accepted to a number of colleges already."

A student, August Clary, described Davis as "a really sweet, smart girl," according to CBS. Clary also knew Pierson since third grade.

"He'd just have bad days sometimes," Clary was quoted as saying. "He would kind of get a little angry with people but I could usually get him to calm down."

"He was kind of quick to aggression but I never saw any physical aggression," said another student.

Pierson's motive is being seen as "some type of retaliation" against a school teacher, according to Robinson.

The sheriff, however, denied earlier reports that Pierson was removed from the school's debate team and suspended from school recently after threatening a teacher, Tracy Murphy, who coaches the debate team. Pierson was subject only to verbal disciplinary action from the teacher, Robinson said.

When Pierson stormed the school Friday, he was reportedly calling out Murphy's name.

"When the teacher heard that this individual was asking for him the teacher exited the school immediately, which was in my opinion the most important tactical decision that could have been made," the sheriff had said earlier.

The shooting took place on the eve of the anniversary of the school shooting in Newtown, Conn., and only about 10 miles from Littleton, where shooters Eric Harris and Dylan Klebold killed 12 students and a teacher at Columbine High School in April 1999 before killing themselves.